Method of plating rolled sheet metal



Oct. 20, 1953 H. A. TOUL Ml N fJR" 2,656,

- METHOD 6F PLATING or LEqsasET METAL Fii d Sept. 7, 1949 37b 38b 9b 40 A INVENTOR ATTORNEYS HARRY A. TOULMIN JR.

Patented Oct. 20, 1953 UNITED STATES r-X'lENT oFFIcE 1 METHOD QF PIQATING ROLLEDSHEET Harry A. Tou1min,-J r., Dayton fihioiassigno tsto 1111!} Commpnwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio A piicnmsstne ta 7, mid-"satin No. 111,320

- cGlaims- This invention relates to the art of deposition ofmetals. Moreparticularly, it relatesto the plating of metals on continuously moving hot metal strip'and apparatus for carrying out the pr e s k In the process of forming steel sheet, one method utilized is the hotr-olling of ingots; "The ingot is formed by casting and rolling to a'slab size of 3 to 6 inches in thickness and ofsuitable width for charginginto a reheating furnace whereit is-brought to a temperature of about 2260 to 2300 F. it v The heated ingot then is passed to thickness reducing mills whereit passes through a roughing train and a finishing train. These mills consist of multiple roller-sand anumben of 'iroll stands depends upon the pressure which it is-desired toexert. Roughing-stands are usually four high and finishing stands were generally. founto eighthigh.

If the rough down is accomplished in areversing universal mill,. the .bar usually,goes through a scale breaker and a'highpressure spray and then into the four high hot strip stands;

In general, the finishing temperature varies from 1300 to l600 F. and must be controlled to provide the desired mechanical properties.

. In the finishing, strip bars of from 8 to 3.2 inches wide andabout inch in'thickness' are heated in a pair furnace to'about the above men- 'tionedil300 to moo s Pairsof bars'al'e withdrawn. from-.this furnace and rolled singly to a predetermined thickness. This. rolled metal is then matched. and rolled "in pairs. r

At the time ofaatatgaepnrg are retain in a sheet furnace and then are rolled tothede sired degree of thinness. As this thinmetal sheet, issues from the last stand of the finishing train, it isat a temperature in approximately the range of 10.00 to 1200113 During the cooling operation .the hot .inetal must be protected from the atmosphere in space consuming complicated equipment in ordento avoid oxide formation, which both'destroys the appearance and adds another stepitothe cleaning operation in order to prepare. the metal for 2 the 'disadvantages and limitations of the esses known heretofore; w It is also an object of'thisinvention to produce plated =rolled sheetsin a relatively inexpensive mam er 1. It isa further object of th invention. to provide a process Which is of lowerloperating cost because itutilizes the heat of the nietal as it"issuesfrom a 'rolling mill for the useful-purpose of 'plating, Whereas this heat normallypresents a cooling problem andis a troublesome factor.- 1.; 1: It-is another object ofithe present inventionto provide a protective coating:-.formed on themetal while still hot whichwi'lllprotect'iron against oxide formation. .o i 4;:

It is a stillfurther. ObjGCt- OfnthiS nvention to provide metal sheet with avariety of1relativelyin- .expensively applied protective metal coatings which are. not deposableby. electrolyticimethods. It is another object of the present. invention to provide .a process wherein .sheetmetalas it issues from the rolling mill may be. continuously plated on both sides.

Another object of this invention is to provide simplified apparatus for carryingout-the above process; I -.-Other'and more specificobjects and advantages will be apparent to oneskilled-in-the-art as the following description proceeds. g -Inbrief-, this inventionv comprises continuously passingsheet -issuing irom ahot rolling mill through a chamberrwhere the heat of the-metal is utilized to decompose metal-bearing gases and todeposit a protective coating.- In this ;way,;at least a portion of the heat in: the metalis utilized instead of being dissipated. 4 7

Further, a coating is deposited which simplifies cooling through the critical temperature range for oxide formation because the iron is no longer exposed. l

It will also be recognized that the process permits-depositing an adhering protective metal coating, such as tungsten, ich cann ns deposited-electrolytically Insequence, the plate is subjected preferably to a reducing atmosphere, although this steps o tional, plating withmetal na arin'aimg to procimpart'ductility. I

Theplating operation maybedividd ihto a preliminaryfl ash coating with metal and a finish plating. operationlin' which event an. adhesion anneal or heating is interspersed between the two coatingoperationsj i T. One of the factorsimportant to thesucce'ssful operaiic te the pretet tm are aware hereinafter described in detail is control of gas pressure in each of the segments of the housing.

In order to insure against leakage of plating gases from the plating chamber or compartment and still have openings in the partition walls for continuous passage of metal sheet, it is necessary to maintain a metal-vapor free gas atmosphere at a slightly higher gas pressure in the housing segments or compartments preceding and succeeding the plating chamber.

The leakage of inert gas into .a plating chamber is limited to small quantities by having apertures in the partition wall of a width providing only a loose sliding fit with the metal sheet passing therethrough and by keeping the pressure difierential small.

It will be recognized that the inert gas leaking into the plating chamber is not a harmful operation because the metal-bearing gases are usually diluted with an inert gaseous medium and the g gas decomposing reaction in the plating chamber produces relatively inert decomposition products such as carbon monoxide.

In the process a stream of gaseous material is brought into contact with the hot metal plate. The gaseous atmosphere may be formed by mixing an inert gas with the vapors of a volatile metal compound or by atomizing a liquid metal compound into a blast of hot inert gas or other equivalent method.

Carbon dioxide, helium, nitrogen, hydrogen, the gaseous product of controlled burning of hydrocarbon gases free of oxygen, and the like, have been utilized as a carrier medium or inert gas medium.

In some instances the use of hydrogen is preferred as, for example, in a first compartment of the housing where its ability to act as a reducing agent may be put to advantage to remove any oxide film on the surface of metal sheet.

Metals to be deposited may be introduced as gaseous metal carbonyls or vaporized solutions of certain of the metal carbonyls in readily vaporizable solvents (for example, petroleum ether), also nitroxyl compounds, nitrosyl carbonyls, metal hydrides, metal alkyls, metal halides, and the like.

Illustrative compounds of the carbonyl'type are nickel, iron, chromium, molybdenum, cobalt, and mixed carbonyls.

Illustrative compounds of other groups are the nitroxyls, such as copper nitroxyl; nitrosyl carbonyls, for example, cobalt nitrosyl carbonyl; hydrides, such as antimony hydride, tin hydride; metal alkyls, such as chromyl'chloride; and carbonyl halogens, for example, osmium carbonyl bromide, ruthenium carbonyl chloride, and the like.

Each material from which a metal may be plated has a temperature at which decomposition is complete. However, decomposition may take place slowly at a lower temperature or while the vapors are being raised in temperature through some particular range. For example, nickel carbonyl completely decomposes at a temperature in the range of 375 F. to-400 F. However, nickel carbonyl starts to decompose slowly at about 175 F. and therefore decomposition continues during the time of heating from 200 F. to 380 F. A large number of the metal carbonyls and hydrides may be effectively and efficiently decomposed at a temperature-in the range of 350 F. to 450 F. When working with most metal carbonyls we prefer to operate'in a temperature range of 375 F. to 425 F.

Maintenance of the metal sheetattemperatures in the general decomposition range is easily accomplished by guiding the metal sheet in timed sequence through a unit where the time for radiation and loss of heat is readily controlled and then directly into the plating apparatus.

For anneals between and after the plating operation the metal sheet may be heated by causing the metal plate to conduct electrictiy or to be heated by induction or other suitable means.

When annealing temperatures, which are considerably higher than plating temperatures, i. e.

in the range of 800 to 1200 F., are to be used, the

operation is preferably carried out by causing the metal sheet to conduct electricity. This generally consists of impressing upon terminals contacting the metal sheet a voltage sufficient to bring the sheet to a red heat.

The lower temperature of the plating area is then accomplished by placing an electrical shunt in parallel with the plating zone. In this way the amount of current passing in the metal sheet is reduced and as a result its temperature quickly lowers to a predetermined range.

With hot metal issuing from a finishing mill there is seldom any need to employ a preparatory surface cleaning operation. However, if one is found necessary conventional methods may be used.

The invention will be more clearly understood from the following description of one embodiment of the apparatus and its mode of operation.

In the drawings:

Figure 1 is a diagrammatic illustration of a complete plate forming and plating unit;

Figure 2 is a vertical front view diagrammatically showing the rollers of a stand and metal being rolled;

Figure 3 isan enlarged sectional view diagrammatically showing the seal used at either the inlet or outlet end of the housing for the plating unit;

Figure 4 is a sectional view diagrammatically illustrating the partition unit separating the housing into segments; and

Figure 5 is a vertical sectional view of the flexible upper leg of the partition divider which yields thus permitting the equipment to accommodate any metal sheet thickness.

Referring to the drawings, there is shown a four high stand ll] of the finishing train of a rolling mill. A strip of metal H composed of paired sheets of iron which have'been heated to about 1300 F. in a pair oven (not shown) is illustrated being fed between the middle rollers l2 of the stand it and issuing as a sheet I3, of desired reduced thickness.

The sheet I3 after suitable delay for cooling about 600 to 700 F. indicated at M by the broken strip, enters a housing l5. Entrance to the housing i5 is made through a seal E6. The rolled plate within the housing 15 passes through the partition units I8 and is drawn out through a seal it which is of roller construction or a seal similar to seal l6. The'strip is wound on suitable spools or reels 20 or otherwise accumulated.

Seal 16 is more fully illustrated in Figure 3 and consists of a trough 2|. This trough is adapted to be filled with a fluid 22, such as mercury, low melting point eutectic fusible alloys, or equivalent fluid. Mounted on the trough 2i is a support 23. Support 23 carries three rollers 2 25 and 26 mounted on ball bearings forfree action.

Support 23 is composed of a vertical portion 27 adapted to extend intothe mercury bath and The support 23 provides atv its extremity the mounting for roller 24.: The leftwardly extending portion of support 23 forms a housing within which roller 26 is free to rotate.

If desired guide rollers 28 may be utilized.

Partition elements !8, asshownmore .in detail in Figures 4 and 5, consist of lower and upper wall members 36 and 3| upon which are mounted through suitable brackets rollers 32 and 33, respectively.

Inasmuch, as the hot metal strip must be supported during its travel, rollers 32 are mounted atop the bottom half of partition wall in fixed position. To provide flexibility in thickness of sheet that may be handled roller 33 is affixed to a movable mounting 34. One version of this mounting adapted to provide gas tight engagement is shown in more detail in Figure 5.

:In this type mounting providing sealing engagement wall 3| acts as a support. Slidab1y engaging wall 3! is a guide 42. This guide 42 supports through suitable brackets bearingsfor roller 33. 1 I I M .f

Wall 3| is also the guide for a bracket 45. Bracket 45 is formed with two channeled leg members 46 and 41. In the legs are held members-48 and 49 yieldingly urged into engagement with the roller-33 by springs 56 and 5|, respectively.

If desired, as an additional precaution against leakage of gas, suitableg'asketingmaterial may be afilxed. Also, if electrical contact is desired suitable conduit may be positioned on wall 3| and attached to a terminal of a brush contact with any of said rollers 33.

Referring again to Figure 1, housing l5 may be divided by partition units l8 into a number of segments, in this case illustrated with five segments 36 to 46, inclusive.

Each segment or compartment is provided with inlet and outlet conduits, as for example 36a and 361).

In brief, the operation of the apparatus is as follows:

Hot rolled sheet l3 issuing from between the rollers I2 after suitable delay move through seal I6 by passing over roller 26 and down through the mercury.

The hot rolled sheet turns upward after passr coated sheetis then accumulatedon reel 2|].

Gas is circulated through each compartment and, under certain circumstances, through compartments joined in series. For example, plating gas may becirculated through the plating compartments 31 and 39 in series, whileinert gas alone may be circulated in compartment 36, 38 and in series.

The gas is generally circulated in counter-current flow to the direction of movement of the sheet being plated. To this end gas is fed to each compartment through an inlet indicated (1 Cir near the point of plate egress from the compartment and an outlet indicated b near the point of ingress into the compartment.

When using a five segment apparatus'for coating described in connection with the drawing, plating gases are excluded from the non-plating sections or compartments by passing through these compartments one or more of the above mentioned inert gases, at rates in the range of 10 to 20 cubic feet per hour per cubic foot of plating chamber.

' In the plating chamber gas flow of mixed gas containing inert gas, such as nitrogen mixed with volatile metal compounds, is at a gas rate in the range of 2 to 5 cubic feet per hour per cubic foot of plating chamber;

In the plating of nickel upon 32 inch wide sheet SAE 4340 of approximately .025 inch in thickness, the following conditions may be main- The temperature of I the sheet entering the plating chamber may be-approximately 425 F., for the anneals between plating and following the last plating step, the rolled sheet maybe heated to approximately 1000 F., rate of flow of carbon dioxide gas through the annealing compartments in series maybe approximately 20' to 40 cubic feet of gas per hour per cubic 'footoi. chamber space.

Rate of fiow of gas through the plating compartments may be approximately 10 to 30'cubic feet per hour per cubic 'foot'of chamber space, with nickel carbonyl vapors being present when it is desired to deposit a nickel plate in the ratio of approximately 10 ounces of carbonyl'pe'r cubic foot of carbon dioxide gas passed through the plating chamber.

It will be understood that while the method and apparatus disclosed and described herein illustrate a preferred form of the invention, modification can be made without departing from the spirit of the invention, and that all modifications that fall within the scope of the appended claims are intended to be included herein.

For example, plating is accomplished in the above apparatus on both sides of the paired sheets. However, when these sheets are separate it will at once be recognized that the individual sheets are only plated on one side. If the paired sheets, however, are split before plating, it will at once become apparent that each individual half sheet can be plated on both sides.

I claim: 7

1. A process of continuously plating a moving hot metal sheet as delivered from a. mill which comprises the steps of guiding said hot metal sheet therealong while heated to a temperature between about 1300 and 1600 F., cooling the same under nonoxidizing atmospheric conditions, said metal sheet being cooled to a temperature which is sufficient to cause decomposition of a heat-decomposable metal. vapor, compound brought in contact therewith, subjecting said hot moving sheet to a plurality of gaseous metal plating treatments, said gaseous metal plating treatments comprising exposing said moving hot sheet in a plating chamber to a gaseous mass at least a portion of which consists of a. heatdecomposable metal vapor compound, said plating chamber having chambers adjacentthereto which are kept under slightly higher gas pressure than in said plating chamber, said sheet being maintained at a temperature sufficient to cause decomposition of said heat-decomposable metal vapor compound and deposition of the iaesaeaa 1'? metal constituent thereof on :said moving ;ho.t metal sheet.

2. A process of rcontinuously plating -a movin-g hot metal sheet as :delivered froma mill which comprises the steps of guiding said L'hOl) metal sheet therealong while heated to a temperature between about 1300and 16.00? F.,- cooling thesame under non-oxidizing atmospheric :conditions said metal sheet being cooled to ,a-temperature which is sufficient to :cause decomposition of .a heatdecomposable metal vapor compound abIfOllght in contact therewith, subjecting said ;hot :moving sheetalternately to a plurality .of gaseous metal plating and heating treatments, said gaseous metal plating treatment comprising subjecting said sheet in a plating chamber to .a heat-decomposable gaseous metal compound, said :plating chamber having chambers iadjacent thereto which are kept underslightlyhigher; gas pressure than in said plating chamber, said sheet being maintained heated ata temperature sufficient to cause decomposition of said gaseous metal :compound and deposition of the metal constituent thereof on said hot sheet, said plating and '.heat treatments being carried out under non-oxidizing atmospheric conditions.

3. A process ofcontinuouslyplating a moving hot metal sheet as delivered from a-lmill which comprises the steps of guiding said :hot metal sheet therealong while heated to a temperature between about 1-300-and1600 F., cooling-thesame under non-oxidizing atmosphericzconditions, said metalsheet being cooled-to a'temperature'which is sufiicient to cause decomposition of .a heatdecomposable metal vapor compound brought in contact therewith, subjecting said not moving sheet to a plurality of gaseous metalplating-treatments, said gaseous 'metal plating treatments comprising continuously exposingsaid hot sheet in a plating chamber to a continuouslyimoving gaseous material composed of carbon dioxide and a heat-decomposable gaseous metal compound, said plating chamber having chambersadjacent thereto which are .kept under slightly ,highergas pressure than in said plating chamber, and wherein said moving metal sheet being maintained at a temperature sufficient to cause decomposition of said gaseous metal compound and deposition of the metal constituent thereof on said hot moving sheet.

4. A process of continuously plating a moving hot metal sheet as delivered from a mill which comprises the steps .of guiding said hot metal sheet therealong while heated to a temperature between about .1300-and 1600 -F., co.oling the same under non-oxidizing atmospheric conditions, said metal sheet being cooled to a .temperature which :is sufficient to cause decomposition .of .a heatdecomposable metal vapor compound brought in contact therewith, subjecting said hot moving sheet in a plating chamber and while :heated .to a temperature suificient to cause decomposition of said gaseous metal compound circulated in contact .therewith and deposition of :the metal constituent thereof on said hot moving sheet, said plating chamber having chambers adjacent thereto which are kept under slightlyhighergas pressure than in said plating chamber, thereafter subjecting said sheet to a heat treatment under non-oxidizing atmospheric conditions asthe same is moved therealong, said heat treatment of the moving sheet being ata temperature substantially higher than that for causing decomposition of said gaseous metal compound.

5. .A process of continuously plating a'moving .hot metal sheet as delivered from ,a rolling mill which comprises the steps of guiding said hot metal sheet ,therealong while heated to a temperaturebetween about 1300 and 1600 F., cooling the same under non-oxidizingatmospheric con- :ditions, said metal sheet being cooled to a temperature which is'sufficient to cause decomposition of a heat-decomposable metal vapor compound brought in contact therewith, subjecting said vhot moving sheet to a plurality of gaseous metal plating treatments, said gaseous metal .platingtreatments comprising exposing said movinghot sheet in ,a plating chamberto a continurouslymovinggaseous mixture of carbon dioxide and nickel carbonyl, saidplating chamber-having chambers adjacent thereto-which are kept under slightly higher gas pressure than in said plating chamber, said sheet being maintained at a temperature sufficient to cause decomposition of the nickel carbonyl ,and deposition of nickel on said hot metal sheet as the same is continuouslyv moved therealong.

6. A process of continuously plating a moving hot metal sheet as delivered :from .a rolling mill which comprises the steps of guiding said hot metal sheet therealong while heated to a temperature between about 1300 and 1600F., cooling the :same under non-oxidizing,atmospheric conditions, said metal sheet'being cooled to a temperature which is sufficient to cause decomposition of a 'heat-decomposableometal vapor compound brought in contact therewith, subjecting said hot moving sheet in a plating chamber to a heat-decomposable gaseous metal compound at a temperature suflicient to cause decomposition of the gaseous metal compound and deposition of the metal constituent thereof on the vhot metal sheet, subjecting the :resultant metal coated :hot sheet :to a temperature substantially above that required to decompose said gaseous metal compound and while maintaining said sheet under non-oxidizing atmospheric conditions-and thereafter cooling said sheet :to a temperature sufficient to cause decomposition of a gaseous metaL-compoundand contacting saidcooled metal sheet in a plating chamber with a heat-decomposable gaseous metal compound .whereby decomposition of -the:gaseous metallcornpound and deposition of the metal constituent thereof on said heated precoated moving sheet is eifected, said plating chambers having chambers adjacent thereto which are maintained ata slightly higher gas pressure than in said plating chambers.

HARRY A. TOULMIN, JR.

Fink July 12, 1949 

1. A PROCESS OF CONTINUOUSLY PLATING A MOVING HOT METAL SHEET AS DELIVERED FROM A MILL WHICH COMPRISES THE STEPS OF GUIDING SAID HOT METAL SHEET THEREALONG WHILE HEATED TO A TEMPERATURE BETWEEN ABOUT 1300 AND 1600* F., COOLING THE SAME UNDER NONOXIDIZING ATMOSPHERIC CONDITIONS, SAID METAL SHEET BEING COOLED TO A TEMPERATURE WHICH IS SUFFICIENT TO CAUSE DECOMPOSITION OF A HEAT-DECOMPOSABLE METAL VAPOR COMPOUND BROUGHT IN CONTACT THEREWITH, SUBJECTING SAID HOT MOVING SHEET TO A PLURALITY OF GASEOUS METAL PLATING TREATMENTS, SAID GASEOUS METAL PLATING TREATMENTS COMPRISING EXPOSING SAID MOVING HOT SHEET IN A PLATING CHAMBER TO A GESEOUS MASS AT LEAST A PORTION OF WHICH CONSISTS OF A HEATDECOMPOSABLE METAL VAPOR COMPOUND, SAID PLATING CHAMBER HAVING CHAMBERS ADJACENT THERETO WHICH ARE KEPT UNDER SLIGHTLY HIGHER GAS PRESSURE THAN IN SAID PLATING CHAMBER, SAID SHEET BEING MAINTAINED AT A TEMPERATURE SUFFICIENT TO CAUSE DECOMPOSITION OF SAID HEAT-DECOMPOSABLE METAL VAPOR COMPOUND AND DEPOSITION OF THE METAL CONSTITUENT THEREOF ON SAID MOVING HOT METAL SHEET. 